A semiconductor wafer (hereinafter, simply referred to as “wafer”) as a substrate is transferred while being accommodated in an airtight container in order to prevent dirt or the like in the air from being adhered thereto. As for such a container, there is used a FOUP (Front Opening Unified Pod) specified by SEMI (Semiconductor Equipment and Material Institute) Standards. The FOUP is a box-shaped container configured to accommodate therein a plurality of wafers. The FOUP includes a housing-shaped main body having an opening at one surface thereof and a cover for covering the opening of the housing-shaped main body.
Generally, in a substrate processing apparatus for performing predetermined processing, e.g., plasma processing, the FOUP is installed at a transfer chamber or the like of the substrate processing apparatus and a wafer accommodated therein is unloaded after the cover of the FOUP is opened. A wafer subjected to the plasma processing is returned to the FOUP.
In this case, a reaction by-product may be adhered to the wafer subjected to the plasma processing. If the wafer to which the reaction by-product is adhered is accommodated in the FOUP, an acid gas may be generated due to chemical reaction between the reaction by-product and moisture in the air inside the FOUP or between a volatile gas generated by volatilization of the reaction by-product and moisture in the air inside the FOUP. The acid gas causes an adverse effect, such as abnormal oxidization of a wiring of the wafer subjected to the plasma processing or the like, on the wafer. Further, ammonia (NH3) in a clean room may enter the FOUP and generate a reaction by-product, e.g., ammonium fluoride or ammonium bromide, due to reaction with the acid gas. In that case, the generated reaction by-product is adhered to an unprocessed wafer and contaminates it.
To cope with that, there is suggested a technique for removing moisture or a volatile gas from the inside of the FOUP. For example, there is suggested a method for removing, by ejection, moisture or a volatile gas from the inside of the FOUP by supplying, when the FOUP is attached to the transfer chamber or the like and the cover is removed, an inert gas or a dry gas toward the opening of the main body from a gas supply port provided at the outside of the FOUP (see, e.g., Japanese Patent Application Publication No. 2003-45933).
Since, however, the opening of the main body of the FOUP is in an open state during the supply of the inert gas or the like, it is difficult for the supplied inert gas or the like to remain inside the main body. Accordingly, the amount of the inert gas or the like used is increased.
Even after all the wafers that have been subjected to the plasma processing are accommodated in the main body and the opening is closed by attaching the cover to the main body, the concentration of moisture in the main body needs to be decreased to a certain level by supplying the inert gas or the like thereinto. However, in the method disclosed in Japanese Patent Application Publication No. 2003-45933, it is difficult to maintain the concentration of the inert gas or the like in the main body, because the supplied inert gas or the like does not remain in the main body. Accordingly, time is required to decrease the concentration of moisture in the main body after the opening is closed, and a throughput is decreased.